This invention relates to accumulation conveyors and, more particularly, to pneumatically controlled accumulation conveyors. The invention is especially useful with high-speed conveyor systems.
In commonly owned U.S. Pat. No. 5,191,967, entitled CONVEYOR SYSTEM HAVING NON-SINGULATING ACCUMULATION CONVEYOR, a pneumatically controlled accumulation conveyor is disclosed which is intended, in part, to overcome problems associated with the accumulation conveyor disclosed in U.S. Pat. No. 3,768,630 issued to Russell A. Inwood et al. for an ACCUMULATOR WITH CONVEYOR OVERRIDE. Inwood et al. provide a series of tandem conveyor zones which are each responsive to actuation of the downstream zones in order to actuate that zone if any downstream zone is being actuated. In an accumulation mode, a case stop is raised and cases accumulate behind the stop to the point of actuating a sensing roller to deactivate an associated zone in order to keep articles closely spaced. However, it accomplishes this result using a shuttle valve associated with each zone, which receives its operating pressure in the appropriate circumstances from a series path extending through one or several downstream shuttle valves. During a clear-out mode, all zones are actuated through such series path. The result is a sluggish response to changes in operating states.
U.S. Pat. No. 5,191,967 overcomes this problem by providing an anti-singulation control which deactivates the driving means of an associated zone if the product sensing means for that zone and all of the product sensing means downstream of that zone sense the presence of product in order to produce an accumulation portion in which no zones are actuated. The control activates the drive means of an associated zone if any of the zones downstream of the associated zone are activated in order to produce a transport portion in which all zones upstream of any actuated zone are actuated to transport product without singulation of any upstream grouped product. The driving means for each zone is connected directly to a source of actuating fluid in order to actuate the drive means directly from the source. This provides an increase in product throughput by avoiding singulation between groups of moving packages in an exceptionally responsive manner because actuation through a series of shuttle valves is avoided. Such control may be embodied in first and second pneumatic devices at each sensing roller. The first pneumatic device responds to product actuating the sensing roller associated with that zone in order to connect the drive means of that zone directly with a source of actuating fluid. The second pneumatic device responds to actuation of the drive means of the downstream zone in order to connect the drive means of the controlled zone directly with a source of actuation fluid irrespective of whether any product is actuating the sensing roller associated with that zone.
In a subsequent development by another, such direct connection with a source of actuating fluid is accomplished in the same manner by attaching a pneumatic solenoid, or cylinder, to the arm of the sensing roller of the controlled zone and actuating the solenoid from the air diaphragm which actuates the drive means of the zone downstream of the controlled zone. With the pneumatic solenoid operatively positioned to engage the sensor valve for the controlled zone, the precise same operation as set forth in the U.S. Pat. No. 5,191,967 is accomplished. When any product sensing roller downstream of a zone does not sense the presence of a product, its sensor valve actuates the air diaphragms in order to drive that zone. This, in turn, actuates the solenoid of the upstream zone which retracts the sensing roller and actuates the sensor valve for that zone which drives the upstream zone. This operation cascades upstream in order to retract the sensor rollers for all zones upstream of a zone that do not sense the presence of product in that zone.
While such retractable sensor pneumatic control scheme is a convenient manner to implement the principles of the invention of the U.S. Pat. No. 5,191,967, it is not without its drawbacks. The mounting of the pneumatic solenoid on the movable arm of the sensor roller is a difficult mounting arrangement, both mechanically and pneumatically, because of the requirement that pneumatic lines be plumbed to a movable member. Furthermore, field retrofit is difficult and time-consuming. An additional difficulty is that packages may have bottom surfaces that are somewhat chamfered or otherwise damaged which creates the possibility that a package in a line of packages accumulating on the accumulation conveyor may not properly actuate a sensing roller. If this occurs, or if a pneumatic solenoid or sensing valve malfunctions, the driving means of all zones upstream of the zone having the malfunction will continue to be actuated resulting in an unacceptable increase in product line pressure.